1. Field of the Invention
This invention relates in general to an RF amplifier, and more particularly to a low noise RF amplifier circuit that provides impedance matching with high gain.
2. Description of Related Art
Today's wireless communications markets are being driven by a multitude of user benefits. Products such as cellular phones, cordless phones, pagers, and the like have freed corporate and individual users from their desks and homes and are driving the demand for additional equipment and systems to increase their utility. As a result digital radio personal communications devices will play an increasingly important role in the overall communications infrastructure in the next decade.
Mixed-signal integration and power management have taken on added importance now that analog and mixed analog-digital ICs have become the fastest-growing segment of the semiconductor industry. Integration strategies for multimedia consoles, cellular telephones and battery-powered portables are being developed, as well as applications for less integrated but highly specialized building blocks that serve multiple markets. These building blocks include data converters, amplifiers and voltage regulators. Makers of amplifiers and regulators often eschew integration in CMOS, but strive for compact size and reduced costs with microminiature packaging.
One important aspect of digital radio personal communications devices is the integration of the RF sections of transceivers. Compared to other types of integrated circuits, the level of integration in the RF sections of transceivers is still relatively low. Considerations of power dissipation, form factor, and cost dictate that the RF/IF portions of these devices evolve to higher levels of integration than is true at present. Nevertheless, there are some key barriers to realizing these higher levels of integration.
For example, there are many applications where it's necessary to provide an RF amplifier at the input of a device for amplifying a signal from a source. For RF amplifiers, good input impendance matching to a source impedance is required for proper signal power transfer from the source to the amplifier. However, this requirement can set the limit on an amplifier's input transconductance thereby eliminating the maximum achievable gain by the amplifier. As a result, good impendance matching in combination with a high gain in excess of that is allowed by the normal input transconductance has been impossible.
It can be seen then that there is a need for an amplifier circuit that provides good impendance matching while providing maximum gain.